DFT study of structure stability and elasticity of wadsleyite II.

The structure and stability properties of wadsleyite II as the new phase of Mg(2)SiO(4) has been studied at high pressure by the DFT method. The pressure range corresponds to the transition zone in the Earth. At zero pressure the calculated lattice parameters of the wadsleyite II structure are a=5.749 Å, b=28.791 Å and c=8.289 Å with the density ρ=3406 kg m(-3). The third order Birch-Murnaghan equation of state has been determined for the structure with isothermal bulk moduli K(T)=160.1 GPa and K(T)'=4.3 at a pressure range up to 50 GPa. The elasticity tensor coefficients C(ij)(P), as well as the compressional and shear wave velocities and their pressure derivatives, have been calculated using the deformation method at a range of pressures up to 25 GPa. The results agree with the experimental data and structure properties of the wadsleyite II model. The properties of the wadsleyite II phase are very close to the wadsleyite phase.